Topic 2: Bacteria Flashcards
Spherical
- spherical or round
- COCCUS
-found in various habitats, including soil, water and human body
Rod-shaped
- e. coli
- BACILLUS
- commonly found in soil, water, and the human intestine
- use gliding motility
- cells joined together in a smooth, unbranched filament, trichomes)
- can also grow in branching filaments (hyphae) (clump= mycelia)
Comma shaped
- curved
- VIBRIO
Spiral-shaped
- bizarre shapes, like telephone cords
- move like corkscrews, rotating clockwise or counterclockwise to go forward or back
- works well in aquatic environments, will find them
Variable
- cant quite identify as having one shape
- called pleiomorphic, multiple shapes
Why can decreasing cell size be an advantage for bacteria?
a higher surface to volume ratio means a greater rate of nutrient/waste exchange, higher metabolic rate, faster growth rate and evolution
Bacteria that are exceptions to the typical size
Thiomargarita namibiensis
Epulopiscium fishelsoni
-both can reach close to a millimeter in length
- advantage of being big, can store more things, inclusion bodies
Things in bacterial cytoplasm (11)
DNA nucleoid
Chromosome-packaging proteins
Enzymes involved in synthesis of DNA, RNA
Regulatory factors
Ribosomes
Plasmid(s)
Enzymes involved in breaking down substrates
Inclusion bodies
Gas vesicles
Magnetosomes
Cytoskeletal structures
DNA Storage
Nucleoid
- largest region in cell
- no membrane surrounds it
- house chromosomes and DNA replication machinery
-uses several mechanisms to reduce space
Inclusion Bodies
accumulations of carbon, nitrogen, sulfur or phosphorus storage compounds
- sulfur globules: store sulfur for energy
- polyhydroxybutyrate (PHB): carbon storage compound
Gas vesicles
Used for buoyancy control
Carboxysomes
location of carbon fixation reactions (using RuBisCO enzyme)
Magnetosomes
associated with direction-finding
Topoisomerase
modify structure of DNA to enable “super
coiling”
Bacterial Cytoskeleton
- keeps everything in right place
- proteins involved in cell wall synthesis (cell division):
*MreB: defines cell shape
*FtsZ: forms ring for cell division - proteins involved in moving internal items
*Par homologues: separate newly replicated chromosomes
Cell envelope
all layers surrounding the cytoplasm of cells
- cytoplasmic membrane
- cell wall
- outer membrane if present
Cell membrane
GENERAL
- All cells have a cytoplasmic membrane
- Separates the interior of the cell from the external environment
STRUCTURE
- Usually composed of a phospholipid bilayer with embedded proteins
- Hydrophobic core
- Hydrophilic surfaces interact with either the external environment or the cytoplasm
- Chemically variable due to changes in fatty acid groups attached to a glycerol backbone
- Connected by ester linkages
- May have sterol-like molecules called “hopanoids” in it to help with stability across temperature ranges
OTHER
- capture energy
- holding sensory systems
Cell Wall
- give cells their shape
- protect them from osmotic lysis/ mechanical forces
- structure: matrix of crosslinked strands of peptidoglycan subunits
- peptidoglycan subunits:
- N-acetylmuramic acid (NAM)
- N-acetylglucosamine (NAG)
- short peptide chain
Peptides and peptide crosslinks vary by species
Peptide crosslinks features
- NAM connects to NAM
- Unusual D-isomers of amino acids in the crosslinks
- Diaminopimelic acid (DAP) in Escherichia coli
- Pentaglycine interbridges within Staphylococcus aureus
Formation of bacteria cell walls
- Bactoprenol transports pentapeptide precursors
- Transglycosylation attaches NAG to NAM
- Transpeptidation connects peptide chains
Gram+ Bacteria
- thick outer layer of peptidoglycan
- variable width periplasmic space
- negatively charged teichoic acids in the peptidoglycan
Gram- bacteria
- very thin layer of peptidoglycan
- periplasmic space of varying width
- outer membrane composed of lipopolysaccharide (LPS)
Gram Stain
Crystal violet stains cells
Iodine traps the colour
Alcohol decolourization shrinks large pores in Gram-positive cells and locks crystal violet stain in
Alcohol strips away some outer membrane lipids in Gram-negative cells
Safranin stains Gram-negative cells pink
Outer Membrane
LPS in Gram-negative outer membrane
- O (outer) side chain of polysaccharides can vary
- Changed by the microbe to evade host immune responses
- Must be careful when treating Gram-negative infections because outer membrane may cloak components that elicit a strong immune response (e.g., Lipid A)
Facilitated diffusion
involves a protein associated with the cytoplasmic membrane enabling a substrate or solute to pass down its concentration gradient into the cell, doesn’t require ATP
co-transport
2 types
Symport: brings something of low concentration in with something of high concentration
Antiport: something with high concentration inside the cell, bring in something with low concentration outside the cell, no ATP required
active transport
uses ATP
transports solutes into cell against concentration gradient using energy from ATP
How do antibiotics target bacteria?
B-lactam inhibits FtsI transpeptidation, interrupting covalent linkages between neighboring peptide chains (in the bacteria, stops cell wall formation)
What is some bacteria’s response to antibiotics, how is that resolved?
- some bacteria produce b-lactamase, interfere with the lactam ring, destroys the b-lactam, so resistant to antibiotic
- resolved by adding clavulanic acid (isn’t antibiotic itself), interferes with and occupies b-lactamase, so b lactam can do its job
Flagella
- spiral, hollow, semi-rigid filaments extending from the cell surface
- locations and number vary across species
- three pieces: filament of flagellin proteins, hook protein, basal body
- energy comes from proton motive forces
Motility of flagella
- Polar flagella: propel forward or backward depending on spin direction
- Amphitrichous: propel one way or another depending on which flagellum spins
- Peritrichous: one direction of rotation moves forward, a change in direction induces a tumble
Chemotaxis
-run and tumble
- either towards chemical attractants or away from repellents
Gliding motility
smooth sliding over a surface
Twitching motility
slow, jerky process using pili that extend, attach to, and pull along a surface
Pili
- fibers of pilin protein, possess other protein on their tips for sticking
- extend outward from cell, allow attachment and twitching motiliy
Stalks
- A “holdfast” of polysaccharides is used to attach an organism to a surface
- Provide extra surface area for nutrient absorption
Capsules
Thick layer of polysaccharides surrounding some cells: adhesion (e.g., biofilms), defense against host immunity, protection against desiccation
Surface arrays (S-layers)
- Crystalline array of interlocking proteins
- Protects cell against predation or infection with bacteriophages
- Found in Gram-positive and Gram-negative cells
